Yeah, you can screw yourself up in fairly minor and temporary ways. BFD. You can screw yourself up doing anything worthwhile physically. Talk to my doctor friend about how many people injure themselves doing yoga, often in ways that are not minor or temporary (downward dog, anybody?).
The orthopod who did my ACL graft/meniscectomy told me he worked on a guy who totally blew his medial meniscus going into lotus position and either on aikiweb or aikido-l yrs ago somebody posted they blew a knee out getting up from the mat.
Life is dangerous but beats the alternative